This invention relates to acoustical sources for use in a liquid environment and more particularly to such sources, called hydro guns, in which slugs of water are propelled into the surrounding water by a piston under the influence of an expanding volume of high pressure pressurized gas, and these slugs of water create cavities which collapse under hydrostatic pressure for creating sharply peaked pressure impulses.
The present invention in one of its applications is advantageous for use in marine life management to prevent marine animals from occupying specific locations where their presence is undesirable. One such application is the diversion of marine animals for example, fish, turtles, manatees and the like away from cooling water intake structures associated with steam generating plants, either fossil fuel or nuclear fuel. Fish are commonly either impinged and trapped on protective nets or screens or are carried into intake systems. In either case, large fish mortality can result with substantial costs being incurred by utilities.
As mentioned above, screens, nets or other types of continuous barriers do not provide a solution to the problem of animal intrusion into cooling water intake structures because of the likelihood of their impingement and trapping as well as the problem of clogging by debris, and the possibility of damage to the barriers caused by ice, logs or boats. In attempting to provide a solution to the above problem in marine life management, lights and sound generators submerged in water have been used to create a field of radiation attempting diversion of marine life from a protected area. Lights often attract rather than repelling marine life, and unattended submerged lights rapidly deteriorate, burn out, break or short circuit.
Among under water sound generators, the seismic airgun is convenient to use and produces high amplitude acoustical radiation. This acoustical energy is mainly generated by airguns at low frequencies (5 to about 200 Hz) and thus produces relatively long acoustical wavelengths. It has been observed that some fish, particularly small fish, will swim quite close to these airguns during operation. It is suggested that the long wave length (acoustical) sound waves produced by these devices do not stimulate an adequate aversion response in small fishes. I believe that acoustical impulses having a steeper wave front, in other words, a higher frequency content than those generated by an airgun would be more effective in modifying small fish behavior. It is also believed that the turbulence and water aeration associated with airgun impulses may act as an attractant to some species of marine life.